A droplet actuator typically includes one or more substrates configured to form a surface or gap for conducting droplet operations. The one or more substrates include electrodes and establish a droplet operations surface or gap for conducting droplet operations. The droplet operations substrate or the gap between the substrates may be coated or filled with a filler fluid that is immiscible with the liquid that forms the droplets. Droplet operations are controlled by the electrodes. In related work, the inventors have used droplet actuators in a variety of applications, including immunoassays (e.g., enzyme linked immunosorbent assays (ELISA)) Immunoassays are among the most sensitive and specific analytical methods that are routinely used in clinical laboratories.
Cardiac markers are commonly measured to evaluate health. For example, cardiac markers may be measured to evaluate heart function or assess heart disease. Among other things, cardiac markers may be measured to assess acute coronary syndromes, identify and manage patients at risk of acute myocardial infarction (AMI), triage patients with chest pain, and/or assess reperfusion status following thrombolytic therapy. Examples of cardiac markers include aspartate transaminase (AST); atrial natriuretic peptide (ANP); brain natriuretic peptide (BNP); brain natriuretic propeptide (proBNP); cardiac troponin (cTn); cardiac troponin complex subunits I, C and T (cTnI, cTnC, cTnT); cardiac cTnIsoforms; C-reactive protein (CRP); creatine kinase-MB (CKMB); C-type natriuretic peptide (CNP); cystatin C (CSC); fatty acid binding protein (FABP); glycogen phosphate isoenzyme BB (GPBB); ischemia-modified albumin (IMA); lactate dehydrogenase (LDH); myeloperoxidase (MPO); Mb (Mb); N-terminal fragment of brain natriuretic propeptide (NT-proBNP); placental growth factor (PIGF); pregnancy-associated plasma protein-A (PAPPA); sCD40 ligand; and various fragments and isoforms of the foregoing.
Measurements of cardiac markers provide a highly effective means of evaluating chest pain, but results of the test are often not available on an immediate-need basis. There is a need for improved methods of multiplexing immunoassays for detection of cardiac markers that provides for small sample size, flexibility in cardiac marker panel design, and real-time diagnosis of these markers.